Wireless power control method and device

ABSTRACT

A wireless power control method in a wireless power transmission device for wirelessly transmitting power to a wireless power reception device. The method includes receiving a first control signal from the wireless power reception device at a first time interval; sensing a current within the wireless power transmission device to generate a second control signal at a second time interval; and controlling a wireless power based on the first control signal and the second control signal, and in which the first time interval is longer than the second time interval.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 16/096,426 filed on Oct. 25, 2018, which is the National Phaseof PCT International Application No. PCT/KR2017/002889 filed on Mar. 17,2017, which claims the priority benefit under 35 U.S.C. § 119(a) toKorean Patent Application No. 10-2016-0059667 filed in the Republic ofKorea on May 16, 2016, all of which are hereby expressly incorporated byreference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless charging technology and,specifically, to a wireless power control method in a wireless powertransmitter, through which power can be stably supplied to a wirelesspower reception device even in abruptly changing power transmissionenvironments, and a device therefor.

Discussion of the Related Art

With the recent rapid development of information communicationtechnology, a ubiquitous society based on information communicationtechnology has emerged.

To access information communication devices anytime and anywhere,sensors equipped with a computer chip having a communication functionneed to be installed in all social facilities. Accordingly, supply ofpower to these devices or sensors becomes anew issue. In addition, anoperation of charging a battery requires time and efforts of a user asthe number of types of portable devices such as Bluetooth handsets andmusic players such as iPods as well as cellular phones abruptlyincreases. As a method for solving such a problem, a wireless powertransmission technology is attracting attention.

Wireless power transmission or wireless energy transfer is a technologyfor wirelessly transmitting electric energy from a transmitter to areceiver using the principle of magnetic induction. Use of an electricmotor or a transformer using the principle of electromagnetic inductionbegan in the 1800s, and methods of transmitting electric energy byradiating radio waves or electromagnetic waves such as lasers have beenattempted. Electric toothbrushes and some electric razors frequentlyused are charged using the principle of electromagnetic induction.

Wireless energy transfer methods developed thus far may be classifiedinto electromagnetic induction, electromagnetic resonance, RFtransmission using a short-wavelength radio frequency, etc.

Electromagnetic induction is a technology using the phenomenon that amagnetic flux generated when two coils are placed in proximity to eachother and then current flows through one coil causes electromotive forceto be generated in the other coil and is rapidly commercialized focusingon small devices such as cellular phones. Electromagnetic inductionallows transmission of up to hundreds of kilowatts and has highefficiency but needs to be placed adjacent to a charger or a floorbecause a maximum transmission distance thereof is 1 cm or less.

Electromagnetic resonance is characterized in that it uses an electricfield or a magnetic field instead of electromagnetic waves or current.Electromagnetic resonance is safe with respect to other electronicdevices or the human body because it is rarely affected by a problemcaused by electromagnetic waves. On the other hand, electromagneticresonance has shortcomings that it can be used only over a limiteddistance and space and has relatively low energy transfer efficiency.

Short-wavelength wireless power transmission, simply RF transmission,uses the fact that energy can be directly transmitted and received inthe form of radio waves. This technique is an RF power transmissionmethod using a rectenna. Rectenna is a compound word of antenna andrectifier and refers to an element which directly converts RF power toDC power. That is, RF power transmission is a technique of converting ACradio waves into DC, and research on commercialization thereof isactively conducted as the efficiency thereof is improved.

Wireless power transmission may be used in various manners for the wholeindustries including IT, railroads, and consumer electronics as well asmobile.

In conventional wireless charging systems, wireless power transmissiondevices receive a feedback signal for power control throughcommunication links established between the wireless power transmissiondevices and wireless power reception devices and dynamically controlpower according to the feedback signal.

For example, in the case of the alliance for wireless power (A4WP)standard supporting electromagnetic resonance, a power receiving unit(PRU) periodically transmits a dynamic characteristic parameter packetincluding required power information to a power transmitting unit (PTU)through a Bluetooth communication channel in a power transmission state.The PTU adaptively controls the intensity of transmitted power on thebasis of the received required power information.

Alternatively, in the power matters alliance (PMA) standard supportingelectromagnetic induction, a wireless power transmitting unit adaptivelycontrols transmitted power on the basis of power control signals, whichincludes an increase signal, a decrease signal and a no-change signal,for example, through in-band communication. Here, the increase signal isa signal for requesting operating frequency increase. When an operatingfrequency increases, the intensity of transmitted power decreases. Thedecrease signal is a signal for requesting operating frequency increase.When an operating frequency decreases, the intensity of transmittedpower increases.

Alternatively, in the wireless power consortium (WPC) standardsupporting electromagnetic induction, a wireless power transmitting unitadaptively controls the intensity of transmitted power on the basis of acontrol error packet received from a wireless power receiving unit atpredetermined intervals in a power transmission stage through in-bandcommunication.

As described above, conventional wireless power control methodsaccording to wireless power transmission standards control the intensityof transmitted power only on the basis of a feedback signal receivedfrom a wireless power receiving unit. When the conventional wirelesspower control methods are applied to wireless power receiving unitswhich rapidly move in a charging area, a power control speed is low andthus accurate power control cannot be performed.

SUMMARY OF THE INVENTION

An object of the present invention devised in view of the aforementionedcircumstances is to provide a wireless power control method in awireless power transmission device, and a device therefor.

Another object of the present invention is to provide a wireless powercontrol method optimized for a wireless power reception device whichrapidly moves in a chargeable area, and a device therefor.

Yet another object of the present invention is to provide a wirelesspower transmission device including a feedback circuit configured toadaptively change an output voltage of a power converter according tothe intensity of current input to the power converter in a state inwhich a power supply voltage is fixed.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

The present invention may provide a wireless power control method and adevice therefor.

A wireless power control method in a wireless power transmission devicefor wirelessly transmitting power to a wireless power reception deviceaccording to one embodiment of the present invention may include:detecting intensity of current flowing between a power supply unitsupplying a fixed voltage and a power converter during powertransmission to the wireless power reception device; and dynamicallycontrolling the output voltage of the power converter according to thedetected intensity of current such that the detected intensity ofcurrent is maintained uniform.

Here, the output voltage of the power converter may be controlled by anoutput voltage of a comparator.

Further, the output voltage of the comparator may be determined by apredetermined reference voltage applied to a negative terminal of thecomparator and a voltage applied to a positive terminal thereof inaccordance with the detected intensity of current.

Further, the voltage applied to the positive terminal of the comparatormay be a voltage applied to a capacitor of an RC circuit whichdetermines a time constant.

For example, the wireless power control method may further includechecking whether a charging mode has changed, wherein, when the chargingmode has changed, anew predefined reference voltage corresponding to thechanged charging mode is applied to the negative terminal of thecomparator.

Alternatively, the wireless power control method may further includechecking whether the class of the wireless power transmission device haschanged, wherein, when the class has changed, a new predefined referencevoltage corresponding to the changed class is applied to the negativeterminal of the comparator.

Alternatively, the wireless power control method may further includechecking whether the category of the wireless power reception device haschanged, wherein, when the category has changed, a new predefinedreference voltage corresponding to the changed category is applied tothe negative terminal of the comparator.

Further, the wireless power control method may further includecontrolling power according to a predetermined feedback signal when thepredetermined feedback signal for power control is received from thewireless power reception device during control of the output voltage ofthe power converter.

Here, the feedback signal may be a dynamic characteristic parameterpacket defined in A4WP standard and received through an out-of-bandcommunication channel.

A wireless power transmission device for wirelessly transmitting powerto a wireless power reception device according to another embodiment ofthe present invention may include: a power converter for converting DCpower received from a power supply unit to specific DC power; and afeedback circuit for controlling the output voltage of the powerconverter such that intensity of current input to the power converter ismaintained uniform.

Here, the feedback circuit may include: a current sensor for detectingintensity of current flowing between the power supply unit and the powerconverter; a comparator for comparing a voltage determined in accordancewith the output current of the current sensor with a predeterminedreference voltage; and a voltage distribution circuit in which theoutput voltage of the power converter is controlled according to theoutput voltage of the comparator.

Further, the output voltage of the comparator may be determined byapplying the reference voltage to a negative terminal of the comparatorand applying a voltage determined in accordance with the output currentof the current sensor to a positive terminal of the comparator.

The voltage applied to the positive terminal of the comparator may be avoltage applied to a capacitor of an RC circuit which determines a timeconstant.

Further, the wireless power transmission device may further include: apower transmitter for generating an AC signal amplified by the outputvoltage of the power converter and wirelessly transmitting the AC signalthrough a transmission coil included therein.

Further, the wireless power transmission device may further include: acontrol communication unit for controlling power on the basis of afeedback signal received from the wireless power reception device whilethe feedback circuit controls the output voltage of the power converter.

Further, when a charging mode has changed, the control communicationunit may control a new predefined reference voltage corresponding to thechanged charging mode to be applied to the negative terminal of thecomparator.

Further, when the category of the wireless power reception device haschanged, the control communication unit may control a new predefinedreference voltage corresponding to the changed category to be applied tothe negative terminal of the comparator.

Further, when the class of the wireless power transmission device haschanged, the control communication unit may control a new predefinedreference voltage corresponding to the changed class to be applied tothe negative terminal of the comparator.

Further, the feedback signal may be a dynamic characteristic parameterpacket defined in A4WP standard and received through an out-of-bandcommunication channel.

Another embodiment of the present invention may provide acomputer-readable recording medium recording a program for executing oneof the above-described wireless power control methods.

The above-described aspects of the present invention are merely some ofpreferred embodiments of the present invention and various embodimentsin which technical features of the present invention are reflected maybe derived and understood by those skilled in the art on the basis ofthe following detailed description of the present invention.

Advantageous Effects

The effects of the method and the device according to the presentinvention are as follows.

The present invention provides a wireless power control method in awireless power transmission device, and a device therefor.

In addition, the present invention provides a wireless power controlmethod optimized for a wireless power reception device which rapidlymoves during charging, and a device therefor.

Furthermore, the present invention provides a wireless powertransmission device including a feedback circuit configured toadaptively change an output voltage of a power converter according tothe intensity of current input to the power converter in a state inwhich a power supply voltage is fixed.

Moreover, the present invention provides a wireless power control methodand a device therefor capable of maintaining the amount of powertransmitted through a transmission coil by maintaining a constantintensity of current input to a power converter through a feedbackcircuit.

Further, the present invention provides a wireless power control methodin a wireless power transmission device capable of preventing in advancethe amount of received power from rapidly changing according to abruptchange in a coupling coefficient of a transmission coil and a receptioncoil.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present disclosure are notlimited to what has been particularly described hereinabove and otheradvantages of the present disclosure will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a system configuration for describing anelectromagnetic resonance wireless power transmission method accordingto an embodiment of the present invention.

FIG. 2 is a diagram for describing a type and characteristics of awireless power transmitter in an electromagnetic resonance methodaccording to an embodiment of the present invention.

FIG. 3 is a diagram for describing a type and characteristics of awireless power receiver in the electromagnetic resonance methodaccording to an embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram of a wireless power transmissionsystem in the electromagnetic resonance method according to anembodiment of the present invention.

FIG. 5 is a state transition diagram for describing a wireless powertransmitter state transition procedure in the electromagnetic resonancemethod according to an embodiment of the present invention.

FIG. 6 is a state transition diagram of a wireless power receiversupporting the electromagnetic resonance method according to anembodiment of the present invention.

FIG. 7 is a diagram for describing an operation region of a wirelesspower receiver according to V_(RECT) in the electromagnetic resonancemethod according to an embodiment of the present invention.

FIG. 8 is a diagram for describing a wireless power control method in aconventional wireless charting system.

FIG. 9 is a block diagram for describing a configuration of a wirelesspower control device according to an embodiment of the presentinvention.

FIG. 10 is a diagram for describing a structure of a wireless powercontrol device including a feedback circuit according to an embodimentof the present invention.

FIG. 11 is a flowchart for describing a wireless power control method ina wireless charging system according to an embodiment of the presentinvention.

FIG. 12 is a flowchart for describing a wireless power control method ina wireless power transmission device according to an embodiment of thepresent invention.

FIG. 13 is a flowchart for describing a wireless power control method ina wireless power transmission device according to another embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A wireless power control method in a wireless power transmitter whichwirelessly transmits power to a wireless power reception deviceaccording to an embodiment of the present invention may include a stepof detecting the intensity of current flowing between a power supplyunit which supplies a fixed voltage and a power converter during powertransmission to the wireless power reception device, and a step ofdynamically controlling an output voltage of the power converteraccording to the detected intensity of current such that the detectedintensity of current is maintained constant.

Reference will now be made in detail to the embodiments, examples ofwhich are illustrated in the accompanying drawings. The suffixes“module” and “unit” of elements herein are used for convenience ofdescription and thus can be used interchangeably and do not have anydistinguishable meanings or functions.

Although all elements constituting the embodiments are described asintegrated into a single one or to be operated as a single one, theembodiments is not necessarily limited to such embodiments. According toembodiments, all of the elements may be selectively integrated into oneor more and be operated as one or more within the object and the scopeof the embodiments. Each of the elements may be implemented asindependent hardware. Alternatively, some or all of the elements may beselectively combined into a computer program having a program moduleperforming some or all functions combined in one or more pieces ofhardware. A plurality of codes and code segments constituting thecomputer program may be easily understood by those skilled in the art towhich the embodiments pertain. The computer program may be stored incomputer readable media such that the computer program is read andexecuted by a computer to implement the embodiments. Computer programstorage media may include magnetic recording media, optical recordingmedia, and carrier wave media.

In description of exemplary embodiments, it will be understood that,when an element is referred to as being “on” or “under” and “before” or“after” another element, the element can be directly on another elementor intervening elements may be present.

The term “comprises”, “includes”, or “has” described herein should beinterpreted not to exclude other elements but to further include suchother elements since the corresponding elements may be included unlessmentioned otherwise. All terms including technical or scientific termshave the same meanings as generally understood by a person havingordinary skill in the art to which the embodiments pertain unlessmentioned otherwise. Generally used terms, such as terms defined in adictionary, should be interpreted to coincide with meanings of therelated art from the context. Unless differently defined in theembodiments, such terms should not be interpreted in an ideal orexcessively formal manner.

It will be understood that, although the terms first, second, A, B, (a),(b), etc. may be used herein to describe various elements of theembodiments, these terms are only used to distinguish one element fromanother element and essential, order, or sequence of correspondingelements are not limited by these terms. It will be understood that whenone element is referred to as being “connected to”, “coupled to”, or“access” another element, one element may be “connected to”, “coupledto”, or “access” another element via a further element although oneelement may be directly connected to or directly access another element.

In the description of the embodiments, a device for wirelesslytransmitting power in a wireless power charging system isinterchangeably used with a wireless power transmitter, a wireless powertransmission device, a wireless power transmission device, a wirelesspower transmitter, a transmission end, a transmitter, a transmissiondevice, a transmission side, a wireless power transmission device, awireless power transmitter, or the like, for convenience of description.

In addition, a device for wirelessly receiving power from a wirelesspower transmission device is interchangeably used with a wireless powerreception device, a wireless power receiver, a wireless power receptiondevice, a wireless power receiver, a reception terminal, a receptionside, a reception device, a receiver, or the like, for convenience ofdescription.

A wireless charging device according to the embodiments may beconfigured in the form of a pad, a holder, an access point (AP), a smalleNB, a stand, a ceiling installation type, a wall-mount type, or thelike or one transmitter may also transmit power to a plurality ofwireless power reception apparatuses.

To this end, a wireless power transmitter may provide at least onewireless power transmission method, for example, an electromagneticinduction method, an electromagnetic resonance method, or the like.

For example, a wireless power transmission method may use variouswireless power transmission standards based on an electromagneticinduction method of generating a magnetic field from a powertransmission end coil to perform charge using an electromagneticinduction principle whereby electricity is induced from a coil of areception end due to influence of the magnetic field. Here, the wirelesspower transmission standard of the electromagnetic induction method mayinclude a wireless charging technology of an electromagnetic inductionmethod defined in the wireless power consortium (WPC) and/or thewireless power consortium (PMA).

As another example, the wireless power transmission method may also usean electromagnetic resonance method of transmitting power to a wirelesspower receiver positioned within a short distance by synchronizing amagnetic field generated in a transmission coil of the wireless powertransmitter with a specific resonance frequency. For example, theelectromagnetic resonance method may include a wireless chargingtechnology defined in the alliance for wireless power (A4WP) standardorganization as a wireless charging technology standard organization.

As another example, the wireless power transmission method may also usea radio frequency (RF) wireless power transmission method of loadinglow-power energy to an RF signal and transmitting power to a wirelesspower receiver positioned at a long distance.

As another example of the embodiments, the wireless power transmitteraccording the embodiments may be designed to support at least two ormore of wireless power transmission methods among the aforementionedelectromagnetic induction method, electromagnetic resonance method, andRF wireless power transmission method.

In this case, the wireless power transmitter may determine a wirelesspower transmission method to be adaptively used for a correspondingwireless power receiver based on a type, state, power requirements, andso on of the wireless power receiver as well as the wireless powertransmission method to be supportable by the wireless power transmitterand the wireless power receiver.

A wireless power receiver according to an embodiment may include atleast one wireless power transmission method and may simultaneously andwirelessly receive power from two or more wireless power transmitters.Here, the wireless power transmission method may include at least one ofthe electromagnetic induction method, the electromagnetic resonancemethod, and the RF wireless power transmission method.

A wireless power receiver according to the present invention may be usedin a small electronic device such as a mobile phone, a smartphone, alaptop computer, a digital broadcast terminal, personal digitalassistants (PDA), a portable multimedia player (PMP), a navigationdevice, an MP3 player, an electric toothbrush, an electronic tag, alighting device, a remote controller, or a float but is not limited andmay be any mobile device including a wireless power reception elementinstalled therein to charge a battery. A wireless power receiveraccording to another embodiment may also be mounted on a vehicle, anunmanned aerial vehicle, an air drone, or the like.

FIG. 1 is a diagram showing a system configuration for describing anelectromagnetic resonance wireless power transmission method accordingto an embodiment of the present invention.

Referring to FIG. 1, a wireless power transmission system may include awireless power transmitter 100 and a wireless power receiver 200.

Although FIG. 1 shows that the wireless power transmitter 100 transmitswireless power to the single wireless power receiver 200, this is merelyone embodiment and the wireless power transmitter 100 according toanother embodiment of the present invention may transmit wireless powerto a plurality of wireless power receivers 200. A wireless powerreceiver 200 according to another embodiment may simultaneously receivewireless power from a plurality of wireless power transmitters 100.

The wireless power transmitter 100 may generate a magnetic field using aspecific power transmission frequency, for example, a resonantfrequency, to transmit power to the wireless power receiver 200.

The wireless power receiver 200 may receive power by tuning to the samefrequency as the power transmission frequency used by the wireless powertransmitter 100.

For example, the frequency used for power transmission may be 6.78 MHz.However, the present invention is not limited thereto.

That is, the power transmitted by the wireless power transmitter 100 maybe delivered to the wireless power receiver 200 which resonates with thewireless power transmitter 100.

The maximum number of wireless power receivers 200 capable of receivingpower from a single wireless power transmitter 100 may be determined onthe basis of a peak transmission power level of the wireless powertransmitter 100, a peak power reception level of the wireless powerreceiver 200, and physical structures of the wireless power transmitter100 and the wireless power receiver 200.

The wireless power transmitter 100 and the wireless power receiver 200may perform bidirectional communication through a frequency banddifferent from a frequency band for wireless power transmission, i.e.,resonant frequency band. For example, a half duplex Bluetooth low energy(BLE) communication protocol may be used for bidirectionalcommunication, but the present invention is not limited thereto.

The wireless power transmitter 100 and the wireless power receiver 200may exchange characteristics and state information thereof, for example,power negotiation information for power control, through bidirectionalcommunication.

For example, the wireless power receiver 200 may transmit predeterminedpower reception state information for controlling a power level receivedfrom the wireless power transmitter 100 to the wireless powertransmitter 100 through bidirectional communication, and the wirelesspower transmitter 100 may dynamically control a transmission power levelon the basis of the received power reception state information.Accordingly, the wireless power transmitter 100 can optimize powertransmission efficiency and provide a function of preventing loads frombeing damaged due to overvoltage, a function of preventing unnecessarypower waste due to undervoltage, and the like.

In addition, the wireless power transmitter 100 may execute a functionof authenticating and identifying the wireless power receiver 200through bidirectional communication, a function of identifying deviceswhich are not compatible or objects which cannot be charged, and afunction of identifying effective loads.

A resonance type wireless power transmission procedure will be describedin more detail with reference to FIG. 1.

The wireless power transmitter 100 may include a power supply unit 110,a power converter 120, a matching circuit 130, a transmission resonator140, a main controller 150 and a communication unit 160. Thecommunication unit may include a data transmitter and a data receiver.

The power supply unit 110 may supply a specific supply voltage to thepower converter 120 according to control of the main controller 150.Here, the supply voltage may be a DC voltage or an AC voltage.

The power converter 120 may convert the voltage received from the powersupply unit 100 to a specific voltage according to control of the maincontroller 150. To this end, the power converter 120 may include atleast one of a DC/DC converter, an AC/DC converter and a poweramplifier.

The matching circuit 130 is a circuit for matching impedances betweenthe power converter 120 and the transmission resonator 140.

The transmission resonator 140 may wirelessly transmit power using aspecific resonant frequency according to a voltage supplied from thematching circuit 130.

The wireless power receiver 200 may include a reception resonator 210, arectifier 220, a DC-DC converter 230, a load 240, a main controller 250and a communication unit 260. The communication unit may include a datatransmitter and a data receiver.

The reception resonator 210 may receive power transmitted according tothe transmission resonator 140 through resonance.

The rectifier 220 may execute a function of converting an AC voltagesupplied from the reception resonator 210 into a DC voltage.

The DC-DC converter 230 may convert a rectified DC voltage into aspecific DC voltage necessary for the load 240.

The main controller 250 may control operations of the rectifier 220 andthe DC-DC converter 230 or generate characteristics and stateinformation of the wireless power receiver 200 and control thecommunication unit 260 to transmit the characteristics and stateinformation of the wireless power receiver 200 to the wireless powertransmitter 100. For example, the main controller 250 may monitor outputvoltages and current intensities at the rectifier 220 and the DC-DCconverter 230 to control the operations of the rectifier 220 and theDC-DC converter 230.

Information on the monitored output voltages and current intensities maybe transmitted to the wireless power transmitter 100 through thecommunication unit 260.

Further, the main controller 250 may determine an overvoltage state oran undervoltage state by comparing the rectified DC voltage with apredetermined reference voltage and, when a system error state isdetected according to the determination result, transmit the detectionresult to the wireless power transmitter 100 through the communicationunit 260.

In addition, upon detection of the system error state, the maincontroller 250 may control the operations of the rectifier 220 and theDC-DC converter 230 in order to prevent the load from being damaged orcontrol the power applied to the load 240 using a predeterminedovercurrent breaking circuit including a switch and (or) a Zener diode.

Although FIG. 1 shows that the main controller 150 or 250 and thecommunication unit 160 or 260 of each of the transmitter and thereceiver are configured as different modules, this is merely anembodiment and the main controller 150 or 250 and the communication unit160 or 260 may be configured as one module.

When an event of adding a new wireless power receiver to a chargingregion during charging, canceling connection with a wireless powerreceiver being charged, completing charging of a wireless powerreceiver, or the like is detected, the wireless power transmitter 100according to an embodiment of the present invention may perform a powerredistribution procedure for other wireless power receivers which arecharging targets. Here, a power redistribution result may be transmittedto connected wireless power receiver(s) through out-of-bandcommunication.

FIG. 2 is a diagram for describing the type and characteristics of awireless power transmitter in the electromagnetic resonance methodaccording to an embodiment of the present invention.

Types and characteristics of a wireless power transmitter and a wirelesspower receiver according to the present invention may be classifiedaccording to classes and categories.

The type and characteristics of the wireless power transmitter may beidentified through the following three parameters.

First, the wireless power transmitter may be identified by a classdetermined according to a maximum intensity of power applied to thetransmission resonator 140.

Here, the class of the wireless power transmitter may be determined bycomparing a maximum value of power P_(TX_IN_COIL) applied to thetransmission resonator 140 with a predefined maximum input powerP_(TX_IN_MAX) per class shown in the following wireless powertransmission class table which is referred to as Table 1 hereinafter.Here, P_(TX_IN_COIL) may be an average real number value obtained bydividing a product of a voltage V(t) and a current I(t) applied to thetransmission resonator 140 for a unit time by the unit time.

TABLE 1 Maximum Minimum category Maximum number of Class input powersupport requirements supportable devices Class 1  2 W 1 × class 1 1 ×class 1 Class 2 10 W 1 × class 3 2 × class 2 Class 3 16 W 1 × class 4 2× class 3 Class 4 33 W 1 × class 5 3 × class 3 Class 5 50 W 1 × class 64 × class 3 Class 6 70 W 1 × class 6 5 × class 3

Classes shown in Table 1 are merely an embodiment and a class may benewly added or deleted. Further, maximum input power, minimum categorysupport requirements and a maximum number of supportable devices mayalso be changed according to the purpose, shape and implementation formof the wireless power transmitter.

For example, referring to Table 1, when a maximum value of powerP_(TX_IN_COIL) applied to the transmission resonator 140 is greater thanP_(TX_IN_MAX) corresponding to class 3 and less than P_(TX_IN_MAX)corresponding to class 4, the class of the wireless power transmittermay be determined as class 3.

Second, the wireless power transmitter may be identified according tominimum category support requirements corresponding to the identifiedclass.

Here, minimum category support requirements may be the number ofsupportable wireless power receivers corresponding to the highestcategory among categories of wireless power receivers supportable by thewireless power transmitter of the corresponding class. That is, theminimum category support requirements may be a minimum number ofmaximum-category devices supportable by the corresponding wireless powertransmitter. Here, the wireless power transmitter may support wirelesspower receivers in all categories corresponding to a maximum category orless according to the minimum category support requirements.

However, if the wireless power transmitter can support wireless powerreceivers in a category higher than the category designated by theminimum category support requirements, supporting the wireless powerreceivers by the wireless power transmitter may not be limited.

For example, referring to Table 1, a wireless power transmitter havingclass 3 needs to support at least one wireless power receiver incategory 5. In this case, the wireless power transmitter can support awireless power receiver 100 corresponding to a lower category than thecategory corresponding to the minimum category support requirements.

In addition, the wireless power transmitter may support a wireless powerreceiver in a higher category upon determining the wireless powertransmitter can support a higher category than the categorycorresponding to the minimum category support requirements.

Third, the wireless power transmitter may be identified by a maximumnumber of supportable devices corresponding to the identified class.Here, the maximum number of supportable devices may be identified by amaximum number of supportable wireless power receivers corresponding tothe lowest category among categories supportable at the correspondingclass, which is simply referred to as a maximum number of supportabledevices hereinafter.

For example, referring to Table 1, a wireless power transmitter havingclass 3 needs to support a maximum of two wireless power receivers ofminimum category 3.

However, when the wireless power transmitter can support more than themaximum number of devices corresponding to the class thereof, supportingmore than the maximum number of devices is not limited.

The wireless power transmitter according to the present invention needsto perform wireless power transmission for at least the numbers definedin Table 1 within available power when there is no particular reason fornot accepting a power transmission request of a wireless power receiver.

For example, the wireless power transmitter may not accept a powertransmission request of a wireless power receiver when no availablepower for accepting the power transmission request remains. Otherwise,the wireless power transmitter may control power adjustment of thewireless power receiver.

Alternatively, the wireless power transmitter may not accept a powertransmission request of a wireless power receiver if the number ofwireless power receivers exceeds the number of supportable wirelesspower receivers when the wireless power transmitter accepts the powertransmission request.

Alternatively, the wireless power transmitter may not accept a powertransmission request of a wireless power receiver when the category ofthe wireless power receiver exceeds the category level supportable atthe class of the wireless power transmitter.

Alternatively, the wireless power transmitter may not accept a powertransmission request of a wireless power receiver when the internaltemperature thereof exceeds a reference value.

Particularly, the wireless power transmitter according to the presentinvention may perform the power redistribution procedure on the basis ofthe amount of currently available power. Here, the power redistributionprocedure may be performed in further consideration of at least one ofthe category, wireless power reception state, required amount of power,priority and the amount of power consumed by a wireless power receiverthat is a power transmission target, which will be described later.

Here, information on at least one of the category, wireless powerreception state, required amount of power, priority and the amount ofpower consumed by the wireless power receiver may be transmitted fromthe wireless power receiver to the wireless power transmitter by meansof at least one control signal through an out-of-band communicationchannel.

Upon completion of the power redistribution procedure, the wirelesspower transmitter may transmit the power redistribution result to thecorresponding wireless power receiver through out-of-band communication.

The wireless power receiver may recalculate estimated time required tocomplete charging on the basis of the received power redistributionresult and transmit the recalculation result to a microprocessor of anelectronic apparatus connected thereto. Subsequently, the microprocessormay control a display included in the electronic apparatus to displaythe recalculated estimated time required to complete charging. Here, thedisplayed estimated time required to complete charging may be controlledto disappear after being displayed on a screen for a predetermined time.

When the estimated time required to complete charging is recalculated, amicroprocessor according to another embodiment of the present inventionmay control the recalculated estimated time required to completecharging to be displayed along with information about the reason forrecalculation. To this end, the wireless power transmitter may transmitthe power redistribution result along with information about the reasonof occurrence of power redistribution to the wireless power receiver.

FIG. 3 is a diagram for describing the type and characteristics of awireless power receiver in the electromagnetic resonance methodaccording to an embodiment of the present invention.

As shown in FIG. 3, average output power P_(RX_OUT) of the receptionresonator 210 may be a real number value obtained by dividing a productof a voltage V(t) and a current I(t) output by the reception resonator210 for a unit time by the unit time.

Categories of wireless power receivers may be defined on the basis ofmaximum output power P_(RX_OUT_MAX) of the reception resonator 210, asshown in the following table 2.

TABLE 2 Category Maximum input power Application example Category 1 TBDBluetooth handset Category 2  3.5 W Feature phone Category 3  6.5 WSmartphone Category 4   13 W Tablet Category 5   25 W Small laptopCategory 6 37.5 W Laptop Category 6   50 W TBD

For example, when charging efficiency in a load stage is 80% or higher,a wireless power receiver in category 3 may supply power of 5 W to acharging port of a load.

The categories shown in Table 2 are merely an embodiment and a categorymay be newly added or deleted. In addition, maximum output power and anapplication example per category may also be changed according to thepurpose, shape and implementation form of a wireless power receiver.

FIG. 4 is an equivalent circuit diagram of a wireless power transmissionsystem supporting the electromagnetic resonance method according to anembodiment of the present invention.

Specifically, FIG. 4 shows interface points in an equivalent circuit atwhich reference parameters which will be described later are measured.

Hereinafter, meanings of the reference parameters shown in FIG. 4 willbe described.

I_(TX) and I_(TX_COIL) refer to a root mean square (RMS) current appliedto a matching circuit (or matching network) 420 of a wireless powertransmitter and an RMS current applied to a transmission resonator coil425 of the wireless power transmitter, respectively.

Z_(TX_IN) refers to an input impedance at the rear end of the matchingcircuit 420 and at the front end of the transmission resonator coil 425.

Z_(TX_IN_COIL) refers to an input impedance at the rear end of thematching circuit 420 and the front end of the transmission resonatorcoil 425.

L1 and L2 refer to an inductance value of the transmission resonatorcoil 425 and an inductance value of a reception resonator coil 427,respectively.

Z_(RX_IN) refers to an input impedance at the rear end of a matchingcircuit 430 of a wireless power receiver and an input impedance at thefront end of a filter/rectifier/load 440 of the wireless power receiver.

A resonant frequency used for the operation of the wireless powertransmission system according to an embodiment of the present inventionmay be 6.78 MHz±15 kHz.

Further, the wireless power transmission system according to anembodiment may provide simultaneous charging, that is, multi-chargingfor a plurality of wireless power receivers. In this case, even when awireless power receiver is newly added or deleted, reception powervariations of remaining wireless power receivers may be controlled notto exceed a predetermined reference value. For example, a receptionpower variation may be ±10% but the present invention is not limitedthereto. If it is impossible to control reception power variations notto exceed the reference value, a wireless power transmitter may notaccept a power transmission request from a newly added wireless powerreceiver.

To maintain reception power variations, a wireless power receiver shouldnot overlap with existing wireless power receivers when the wirelesspower receiver is added or deleted.

When the matching circuit 430 of the wireless power receiver isconnected to the rectifier, the real part of Z_(TX_IN) may be inverselyproportional to load resistance of the rectifier, which is referred toas R_(RECT) hereinafter. That is, increase in R_(RECT) may decreaseZ_(TX_IN), and decrease in R_(RECT) may increase Z_(TX_IN).

Resonator coupling efficiency according to the present invention may bea maximum power reception ratio calculated by dividing power transferredfrom a reception resonator coil to the load 440 by power applied by thetransmission resonator coil 425 to a resonant frequency band. Resonatorcoupling efficiency between the wireless power transmitter and thewireless power receiver may be calculated when the reference portimpedance Z_(TX_IN) of the transmission resonator perfectly matches thereference port impedance Z_(RX_IN) of the reception resonator.

The following table 3 shows an example of minimum resonator couplingefficiencies according to classes of wireless power transmitters andclasses of wireless power receivers according to an embodiment of thepresent invention.

TABLE 3 Category 1 Category 2 Category 3 Category 4 Category 5 Category6 Category 7 Class 1 N/A N/A N/A N/A N/A N/A N/A Class 2 N/A 74%(−1.3)74%(−1.3) N/A N/A N/A N/A Class 3 N/A 74%(−1.3) 74%(−1.3) 76%(−1.2) N/AN/A N/A Class 4 N/A 50%(−3)  65%(−1.9) 73%(−1.4) 76%(−1.2) N/A N/A Class5 N/A 40%(−4)  60%(−2.2) 63%(−2)  73%(−1.4) 76%(−1.2) N/A Class 5 N/A30%(−5.2) 50%(−3)  54%(−2.7) 63%(−2)  73%(−1.4) 76%(−1.2)

If a plurality of wireless power receivers is used, minimum resonatorcoupling efficiencies corresponding to the classes and categories shownin Table 3 may increase.

FIG. 5 is a state transition diagram for describing a state transitionprocedure in a wireless power transmitter supporting the electromagneticresonance method according to an embodiment of the present invention.

Referring to FIG. 5, states of a wireless power transmitter may includea configuration state 510, a power save state 520, a low power state530, a power transfer state 540, a local fault state 550 and a latchingfault state 560.

When power is applied to the wireless power transmitter, the wirelesspower transmitter may switch to the configuration state 510. When apredetermined rest timer expires or an initialization procedure iscompleted in the configuration state 510, the wireless power transmittermay switch to the power save state 520.

In the power save state 520, the wireless power transmitter may generatea beacon sequence and transmit the beacon sequence through a resonantfrequency band.

Here, the wireless power transmitter may control the beacon sequence tostart within a predetermined time after transition to the power savestate 520. For example, the wireless power transmitter may control thebeacon sequence to start within 50 ms after transition to the power savestate 520. However, the present invention is not limited thereto.

In the power save state 520, the wireless power transmitter mayperiodically generate and transmit a first beacon sequence for detectinga wireless power receiver and detect an impedance variation of areception resonator, that is, a load variation. Hereinafter, the firstbeacon and the first beacon sequence are referred to as a short beaconand a short beacon sequence for convenience of description.

Particularly, the short beacon sequence may be repeatedly generated andtransmitted at predetermined intervals t_(CYCLE) for a short periodt_(SHORT_BEACON) such that standby power of the wireless powertransmitter can be saved until a wireless power receiver is detected.For example, t_(SHORT_BEACON) may be set to 30 ms or less and t_(CYCLE)may be set to 250 ms±5 ms. Further, the current intensity of the shortbeacon may be equal to or greater than a predetermined reference valueand may gradually increase for a predetermined period of time. Forexample, minimum current intensity of the short beacon may be set to asufficiently large value such that wireless power receivers in category2 or higher in Table 2 can be detected.

The wireless power transmitter according to the present invention mayinclude a predetermined sensing means for sensing variations inreactance and resistance in a reception resonator according to the shortbeacon.

Furthermore, in the power save state 520, the wireless power transmittermay periodically generate and transmit a second beacon sequence forsupplying sufficient power necessary for booting and response of awireless power receiver. Hereinafter, the second beacon and the secondbeacon sequence are referred to as a long beacon and a long beaconsequence for convenience of description.

That is, booting of a wireless power receiver is completed through thesecond beacon sequence, the wireless power receiver may broadcast apredetermined response signal through an out-of-band communicationchannel.

Particularly, the long beacon sequence may be generated and transmittedat predetermined intervals t_(LONG_BEACON_PERIOD) for a long periodt_(LONG_BEACON) longer than the short beacon such that sufficient powernecessary for booting of the wireless power receiver is supplied. Forexample, t_(LONG_BEACON) may be set to 105 mx+5 ms,t_(LONG_BEACON_PERIOD) may be set to 850 ms, and the current intensityof the long beacon may be stronger than the current intensity of theshort beacon. Further, the long beacon may maintain power ofpredetermined intensity for a transmission period.

Thereafter, the wireless power transmitter may wait for reception of apredetermined response signal for a long beacon transmission periodafter detection of an impedance variation in a reception resonator.Hereinafter, the response signal is referred to as an advertisementsignal for convenience of description. Here, a wireless power receivermay broadcast the advertisement signal through an out-of-bandcommunication frequency band different from the resonant frequency band.

For example, the advertisement signal may include at least one ofmessage identification information for identifying a message defined inthe corresponding out-of-band communication standard, service orwireless power receiver identification information for identifyingwhether a wireless power receiver is valid or compatible with acorresponding wireless power transmitter, information on output power ofthe wireless power receiver, information on a rated voltage/currentapplied to a load, antenna gain information of the wireless powerreceiver, information for identifying the category of the wireless powerreceiver, wireless power receiver authentication information,information about whether an overvoltage protection function isprovided, and information on the version of software installed in thewireless power receiver.

Upon reception of the advertisement signal, the wireless powertransmitter may establish an out-of-band communication link with thewireless power receiver after switching to the low power state 530 fromthe power save state 520. Subsequently, the wireless power transmittermay perform a procedure of registering the wireless power receiverthrough the established out-of-band communication link. For example,when out-of-band communication is Bluetooth low-power communication, thewireless power transmitter may perform Bluetooth pairing with thewireless power receiver and exchange at least one of state information,characteristic information and control information with the wirelesspower receiver through the paired Bluetooth link.

When the wireless power transmitter transmits a predetermined controlsignal for starting charging, that is, a predetermined control signalfor requesting the wireless power receiver to transfer power to a load,to the wireless power receiver through out-of-band communication in thelow power state 530, the state of the wireless power transmitter mayswitch from the low power state 530 to the power transfer state 540.

If the out-of-band communication link establishment procedure or theregistration procedure is not normally completed in the low power state530, the state of the wireless power transmitter may switch from the lowpower state 530 to the power save state 520.

In the wireless power transmitter, a separate link expiration timer forconnection with each wireless power receiver may be operated. A wirelesspower receiver needs to transmit a predetermined message indicatingpresence thereof to the wireless power transmitter at predeterminedintervals before expiration of the link expiration timer. The linkexpiration timer is reset whenever the message is received and theout-of-band communication link established between the wireless powertransmitter and the wireless power receiver can be maintained.

If all link expiration timers corresponding to out-of-band communicationlinks established between the wireless power transmitter and one or morewireless power receivers expire in the low power state 530 or the powertransfer state 540, the state of the wireless power transmitter mayswitch to the power save state 520.

Further, the wireless power transmitter in the low power state 530 maydrive a predetermined registration timer upon reception of a validadvertisement signal from a wireless power receiver. Here, when theregistration timer expires, the wireless power transmitter may switch tothe power save state 520. Here, the wireless power transmitter mayoutput a predetermined notification signal for indicating failure ofregistration through a notification means, for example, an LED lamp, adisplay screen, a beeper or the like, included in the wireless powertransmitter.

Further, when charging of all wireless power receivers connected to thewireless power transmitter is completed in the power transfer state 540,the wireless power transmitter may switch to the low power state 530.

Particularly, the wireless power transmitter may permit registration ofa new wireless power receiver in states other than the configurationstate 510, the local fault state 550 and the latching fault state 560.

Further, the wireless power transmitter may dynamically control transferpower on the basis of state information received from a wireless powerreceiver in the power transfer state 540.

Here, receiver state information transmitted from a wireless powerreceiver to the wireless power transmitter may include at least one ofinformation on required power, information on a voltage and/or a currentmeasured at the rear end of a rectifier, charging state information,information for notifying of overcurrent, overvoltage and/or overheatstates, and information indicating whether a means for blocking orreducing power transferred to a load according to overcurrent orovervoltage has been activated. Here, the receiver state information maybe transmitted in a predetermined period or transmitted whenever aspecific event occurs. Further, the aforementioned means for blocking orreducing power transferred to a load according to overcurrent orovervoltage may be provided using at least one of an ON/OFF switch and aZener diode.

Receiver state information transmitted from a wireless power receiver toa wireless power transmitter according to another embodiment of thepresent invention may further include at least one of informationindicating that an external power supply has been connected to thewireless power receiver in a wired manner and information indicatingthat an out-of-band communication method has been changed, for example,change from NFC (Near Field Communication) to BLE (Bluetooth Low Energy)communication.

A wireless power transmitter according to another embodiment of thepresent invention may adaptively determine power intensity per wirelesspower receiver on the basis of at least one of power currently availablefor the wireless power transmitter, priority per wireless power receiverand the number of connected wireless power receivers. Here, the powerintensity per wireless power receiver may be determined as a ratio ofpower required to be received to maximum power which can be processed bya rectifier of the corresponding wireless power receiver.

Here, priority per wireless power receiver may be determined accordingto intensity of power required by a receiver, receiver type, whether thereceiver is currently used, current charge amount, the amount of powercurrently consumed, and the like. However, the present invention is notlimited thereto. For example, priority per receiver type may bedetermined in the order of a cellular phone, a tablet, a Bluetoothheadset and an electric toothbrush. However, the present invention isnot limited thereto. As another example, when a receiver is currentlyused, the receiver may be assigned higher priority than priorityassigned to a receiver which is not used. As another example, higherpriority may be assigned to a receiver when the receiver requires higherpower. As another example, priority may be determined on the basis of acurrent charge amount of a load, that is, remaining charge amount, inthe corresponding receiver. As another example, priority may bedetermined on the basis of the amount of power currently consumed.Further, priority may be determined by at least one combination of theaforementioned priority determination factors.

Thereafter, the wireless power transmitter may transmit a predeterminedpower control command including information about the determined powerintensity to the corresponding wireless power receiver. Here, thewireless power receiver may determine whether power can be controlledwith the power intensity determined by the wireless power transmitterand transmit a determination result to the wireless power transmitterthrough a predetermined power control response message.

A wireless power receiver according to another embodiment of the presentinvention may transmit predetermined receiver state informationindicating whether wireless power control is possible according to apower control command of the wireless power transmitter prior toreception of the power control command.

The power transfer state 540 may be one of a first state 541, a secondstate 542 and a third state 543 according to a power reception state ofa connected wireless power receiver.

For example, the first state 541 may refer to a state in which the powerreception states of all wireless power receivers connected to thewireless power transmitter are normal voltages.

The second state 542 may refer to a state in which the power receptionstate of at least one wireless power receiver connected to the wirelesspower transmitter is a low voltage state and there is no wireless powerreceiver in a high voltage state.

The third state 543 may refer to a state in which the power receptionstate of at least one wireless power receiver connected to the wirelesspower transmitter is a high voltage state.

The wireless power transmitter may switch to the latching fault state560 when a system error is detected in the power save state 520, the lowpower state 530 or the power transfer state 540.

The wireless power transmitter in the latching fault state 560 mayswitch to the configuration state 510 or the power save state 520 upondetermining that all wireless power receivers connected thereto havebeen eliminated from a charging region.

Further, the wireless power transmitter in the latching fault state 560may switch to the local fault state 550 when a local fault is detected.Here, the wireless power transmitter in the local fault state 550 mayswitch to the latching fault state 560 again when the local fault iscanceled.

When the wireless power transmitter has switched from any one of thepower save state 520, the low power state 530 and the power transferstate 540 to the local fault state 550, the wireless power transmittermay switch to the configuration state 510 upon cancellation of a localfault.

When the wireless power transmitter has switched to the local faultstate 550, power supplied to the wireless power transmitter may be cut.For example, the wireless power transmitter may switch to the localfault state 550 when a fault such as overvoltage, overcurrent oroverheat is detected. However, the present invention is not limitedthereto.

For example, the wireless power transmitter may transmit a predeterminedpower control command for decreasing the intensity of power received bya wireless power receiver to at least one wireless power receiverconnected thereto when overvoltage, overcurrent or overheat is detected.

Alternatively, the wireless power transmitter may transmit apredetermined control command for stopping charging of wireless powerreceivers to at least one wireless power receiver connected thereto whenovervoltage, overcurrent or overheat is detected.

The wireless power transmitter may prevent device damage due toovervoltage, overcurrent or overheat through the above-described powercontrol procedure.

The wireless power transmitter may switch to the latching fault state560 when the intensity of output current of the transmission resonatoris equal to or greater than a reference value. Here, the wireless powertransmitter which has switched to the latching fault state 560 mayattempt to perform an operation such that the intensity of outputcurrent of the transmission resonator becomes less than the referencevalue for a predetermined time. Here, the attempt may be repeated by apredetermined number of times. When the latching fault state 560 is notcanceled in spite of repeated attempts, the wireless power transmittermay transmit a predetermined notification signal indicating that thelatching fault state 560 is not canceled to a user using a predeterminednotification means. Here, all wireless power receivers positioned in thecharging region of the wireless power transmitter are eliminated fromthe charging region by the user, the latching fault state 560 may becanceled.

On the other hand, when the intensity of output current of thetransmission resonator decreases to below the reference value within thepredetermined time or while the attempt is performed the predeterminednumber of times, the latching fault state 560 may be automaticallycanceled. Here, the state of the wireless power transmitterautomatically switches from the latching fault state 560 to the powersave state 520 and thus a procedure of detecting and identifyingwireless power receivers may be performed again.

The wireless power transmitter in the power transfer state 540 maycontinuously transmit power and adaptively control transmitted power onthe basis of state information of a wireless power receiver andpredefined optimal voltage region setting parameters.

For example, the optimal voltage region setting parameters may includeat least one of a parameter for identifying a low voltage region, aparameter for identifying an optimal voltage region, a parameter foridentifying a high voltage region and a parameter for identifying anovervoltage region.

The wireless power transmitter may increase transmitted power when thepower reception state of a wireless power receiver is in a low voltageregion and decrease transmitted power when the power reception state isin a high voltage region.

Further, the wireless power transmitter may control transmitted powersuch that power transmission efficiency is maximized.

In addition, the wireless power transmitter may control transmittedpower such that a deviation in the amount of power required by awireless power receiver becomes less than a reference value.

Furthermore, the wireless power transmitter may stop power transmissionwhen a rectifier output voltage of a wireless power receiver arrives ata predetermined overvoltage region, that is, when an overvoltage isdetected.

FIG. 6 is a state transition diagram of a wireless power receiversupporting the electromagnetic resonance method according to anembodiment of the present invention.

Referring to FIG. 6, states of the wireless power receiver may include adisable state 610, a boot state 620, an enable state (or on state) 630and a system error state 640.

Here, a state of the wireless power receiver may be determined on thebasis of the intensity of an output voltage, which is referred to asV_(RECT) for convenience of description, at a rectifier of the wirelesspower receiver.

The enable state 630 may be divided into an optimum voltage state 631, alow voltage state 632 and a high voltage state 633 according to thevalue of V_(RECT).

The wireless power receiver in the disable state 610 may switch to theboot state 620 when a measured value of V_(RECT) is equal to or greaterthan a predefined value of V_(RECT_BOOT).

In the boot state 620, the wireless power receiver may establish anout-of-band communication link with a wireless power transmitter andwait until V_(RECT) reaches power required by a load.

The wireless power receiver in the boot state 620 may switch to theenable state 630 and start charging upon confirmation that V_(RECT) hasreached the power required by the load.

The wireless power receiver in the enable state 630 may switch to theboot state 620 upon confirmation of completion of charging or suspensionof charging.

Further, the wireless power receiver in the enable state 630 may switchto the system error state 640 when a predetermined system error isdetected. Here, system errors may include predefined system errorconditions as well as overvoltage, overcurrent and overheat.

In addition, the wireless power receiver in the enable state 630 mayswitch to the disable state 610 when V_(RECT) decreases to belowV_(RECT_BOOT).

Further, the wireless power receiver in the boot state 620 or the systemerror state 640 may switch to the disable state 610 when V_(RECT)decreases to below V_(RECT_BOOT).

Hereinafter, state transition of the wireless power receiver in theenable state 630 will be described in detail with reference to FIG. 7.

FIG. 7 is a diagram for describing an operation region of a wirelesspower receiver according to V_(RECT) in the electromagnetic resonancemethod according to an embodiment of the present invention.

Referring to FIG. 7, the wireless power receiver is maintained in thedisable state 610 when V_(RECT) is less than V_(RECT_BOOT).

When V_(RECT) increases to over V_(RECT_BOOT), the wireless powerreceiver may switch to the boot state 620 and broadcast an advertisementsignal within a previously designated time. Thereafter, when theadvertisement signal is detected by a wireless power transmitter, thewireless power transmitter may transmit a predetermined connectionrequest signal for establishing an out-of-band communication link to thewireless power receiver.

The wireless power receiver may wait until V_(RECT) reaches a minimumoutput voltage at the rectifier for normal charging, which is referredto as V_(RECT_MIN) for convenience of description, when the out-of-bandcommunication link is normally established and registration issuccessfully performed.

When V_(RECT) exceeds V_(RECT_MIN), the state of the wireless powerreceiver may switch from the boot state 620 to the enable state 630 andstart charging.

If V_(RECT) exceeds V_(RECT_MAX) which is a predetermined referencevalue for determining an overvoltage in the enable state 630, thewireless power receiver may switch to the system error state 640 fromthe enable state 630.

Referring to FIG. 7, the enable state 630 may be divided into the lowvoltage state 632, the optimum voltage state 631 and the high voltagestate 633 according to the value of V_(RECT).

The low voltage state 632 may refer to a state in whichV_(RECT_BOOT)<=V_(RECT)<=V_(RECT_MIN), the optimum voltage state 631 mayrefer to a state in which V_(RECT_MIN)<V_(RECT)<=V_(RECT_HIGH) and thehigh voltage state 633 may refer to a state in whichV_(RECT_HIGH)<V_(RECT)<=V_(RECT_MAX).

Particularly, the wireless power receiver switched to the high voltagestate 633 may reserve an operation of cutting power supplied to a loadfor a previously designated time, which is referred to as a high voltagestate maintenance time for convenience of description. Here, the highvoltage maintenance time may be determined in advance such that thewireless power receiver and the load are not damaged in the high voltagestate 633.

The wireless power receiver may transmit a predetermined messageindicating generation of overvoltage to the wireless power transmitterthrough the out-of-band communication link within a previouslydesignated time upon switching to the system error state 640.

Further, the wireless power receiver may control a voltage applied tothe load using an overvoltage cutoff means included therein in order toprevent the load from being damaged due to overvoltage in the systemerror state 640. Here, an ON/OFF switch and/or a Zener diode may be usedas the overvoltage cutoff means.

Although the method and means for coping with a system error in awireless power receiver when overvoltage is generated in the wirelesspower receiver and thus the wireless power receiver switches to thesystem error state 640 have been described in the above-describedembodiment, this is merely an embodiment and a wireless power receivermay also switch to the system error state due to overheat or overcurrentgenerated in the wireless power receiver in other embodiments of thepresent invention.

For example, when the wireless power receiver switches to the systemerror state due to overheat, the wireless power receiver may transmit apredetermined message indicating generation of overheat to the wirelesspower transmitter. Here, the wireless power receiver may reduce heatgenerated therein by driving a cooling fan or the like included therein.

A wireless power receiver according to another embodiment of the presentinvention may receive wireless power in association with a plurality ofwireless power transmitters. In this case, the wireless power receivermay switch to the system error state 640 upon determining that awireless power transmitter determined to actually transmit wirelesspower to the wireless power receiver differs from a wireless powertransmitter with which an actual out-of-band communication link has beenestablished.

FIG. 8 is a diagram for describing a wireless power control method in aconventional wireless charging system.

Specifically, FIG. 8 is a diagram for describing a wireless powercontrol method in a wireless charging system which transmits a feedbacksignal through out-of-band communication.

Referring to FIG. 8, power supplied from a power supply unit 811 of awireless power transmitter 810 is converted into specific DC powerthrough a DC-DC converter 812. An AC amplifier 813 generates an AC powersignal according to the converted DC power and transfers the AC powersignal to a transmission coil 814. The AC power signal transmittedthrough the transmission coil 814 is received by a reception coil 821 ofa wireless power receiver 820 and transferred to a rectifier 822. OutputDC power of the rectifier 822 is transferred to a DC-DC converter 823and converted into specific DC power required by a load 824.

Particularly, the conventional wireless power receiver 820 may monitorinformation about output power/voltage/current of the rectifier 822 andinformation about power/voltage/current transferred to the load 824. Acontrol communication unit 826 of the wireless power receiver 820 mayperiodically transmit a predetermined power control request signalincluding a monitoring result to a control communication unit 816 of thewireless power transmitter 810 through out-of-band communication. Forexample, the predetermined power control request signal including amonitoring result may be a dynamic characteristic parameter packetdefined in A4WP standard and out-of-band communication may be Bluetoothlow energy communication at 2.4 GHz.

The control communication unit 816 of the wireless power transmitter 810may dynamically control output power of the DC-DC converter 812 on thebasis of the received power control request signal.

That is, the conventional wireless power transmitter 810 controlstransmitted power on the basis of a feedback signal received from thewireless power receiver 820. Although a time required to actuallycontrol power on the basis of a feedback signal may vary according to afeedback signal transmission period, for example, 1.5 seconds or more isrequired, in general.

However, the conventional wireless transmitted power control methodusing a feedback signal has a problem that a feedback signaltransmission period is not short enough to effectively controltransmitted power in a situation in which a coupling coefficient betweenthe transmission coil 814 and the reception coil 821 rapidly changes.Accordingly, it is impossible to provide appropriate power required by areceiver in a situation in which a coupling coefficient rapidly changeswith a conventional wireless transmitted power control speed based on afeedback signal.

In the case of electromagnetic resonance, an impedance level at thetransmission coil increases when the coupling coefficient between thetransmission coil and the reception coil decreases. On the contrary, theimpedance level at the transmission coil decreases when the couplingcoefficient between the transmission coil and the reception coilincreases.

Power transmission efficiency R_efficiency between the transmission coiland the reception coil is proportional to the coupling coefficient K ofthe transmission coil and the reception coil, Q_factor (Q_(t)) of thetransmitter and Q_factor (Q_(r)) of the receiver, as represented by thefollowing expression 2.

R_efficiency=K ² Q _(t) Q _(r)  Expression 2:

As represented by Expression 2, power transmission efficiency decreasesas the coupling coefficient between the transmission coil and thereception coil decreases and increases as the coupling coefficientincreases.

That is, the phenomenon that the intensity of power received by thewireless power receiver decreases when the coupling coefficient betweenthe transmission coil and the reception coil decreases is caused bydecrease in the intensity of transmitted power and decrease in powertransmission efficiency between the transmission coil and the receptioncoil when the impedance of the transmission coil increases.

For example, the coupling coefficient between the transmission coil andthe reception coil may rapidly change to 0.1→0.05→0.2→0.01→0.3 for 0.5seconds, during which the wireless power receiver rapidly moves. If afeedback signal is transmitted and thus power control is performed whenthe receiver has moved to a position at which the coupling coefficientis 0.1, and then the next feedback signal is transmitted when thereceiver has moved to a position at which the coupling coefficient is0.3, power control cannot be normally performed at positionscorresponding to coupling coefficients of 0.05 and 0.01. That is,appropriate power may not be transmitted to the receiver at positionscorresponding to coupling coefficients of 0.05 and 0.01.

FIG. 9 is a block diagram for describing a configuration of a wirelesspower control device according to an embodiment of the presentinvention.

Referring to FIG. 9, the wireless power control device 900 may include apower supply unit 910, a power converter 920, a power transmitter 930and a feedback circuit 940.

The feedback circuit 940 may control an output voltage V_out of thepower converter 920 by detecting the intensity of current I_in flowingbetween the power supply unit 910 and the power converter 920.

Although a detailed configuration of the feedback circuit 940 accordingto an embodiment will be described later in detail with reference toFIG. 10, the present invention is not limited thereto and any circuitcapable of controlling the output voltage of the power converter 920such that the intensity of current input to the power converter 920 iskept uniform may be used as the feedback circuit 940.

Alternatively, the feedback circuit 940 is required only to maintain theamount of power transmitted through a transmission coil uniformirrespective of changes in the coupling coefficient between thetransmission coil and a reception coil.

The power transmitter 930 may include a frequency generator forgenerating an AC signal having a specific frequency, an amplificationcircuit for amplifying the generated AC signal using an output DCvoltage of the power converter, and a transmission coil for wirelesslytransmitting the amplified AC signal. Further, the power transmitter 930may further include a matching circuit for matching impedances betweenthe power converter 920 and the transmission coil.

For example, it is assumed that the rated output power of the powersupply unit 910 is 5 W and the output voltage thereof is 5V. Here, it isassumed that the power converter 920 converts DC 5V into DC 2.5V.

To maintain the intensity of power transmitted through the powertransmitter 930 at 5 W, the intensity of current transferred from thepower converter 920 to the power transmitter 930 needs to be maintainedat 2A (5 W/2.5V) and the intensity of current applied from the powersupply unit 910 to the power converter 920 needs to be maintained at 1A.

However, when the coupling coefficient between the transmission coil andthe reception coil rapidly increases, the quantity of currenttransferred to the power transmitter 930 may rapidly increase and thuspower equal to or greater than 5 W which is the rated output power ofthe power supply unit 910 may be required. In this case, the powertransmitter may stop power transmission to a corresponding wirelesspower receiver.

To solve the aforementioned problem that power transmission is stopped,the wireless power control device 900 according to an embodiment of thepresent invention may adaptively decrease the output voltage V_out ofthe power converter 920 through the feedback circuit 940 to control thepower of 5 W to be maintained when the quantity of current transferredto the power transmitter 930, that is, the intensity of current I_ininput to the power converter 920 rapidly increases. FIG. 10 is a diagramfor describing a structure of a wireless power control device includinga feedback circuit according to another embodiment of the presentinvention.

The wireless power control device according to the present embodimentmay operate by being included in a wireless power transmission device.

Referring to FIG. 10, the wireless power control device may include apower supply unit 1010, a DC-DC converter 1020, a power transmitter1030, a current sensor 1040, a comparator 1050, an RC circuit 1060 andan output voltage control circuit 1070.

The current sensor 1040 may detect the intensity of current I_in inputto the DC-DC converter 1020 in real time by measuring a voltage appliedto a fifth resistor R5 positioned between the power supply unit 1010 andthe DC-DC converter 1020.

The current sensor 1040 may transmit current I_s corresponding to thedetected intensity of current I_in to the RC circuit 1060.

The RC circuit 1060, which is a circuit for controlling a rate of changeof a voltage V_c applied to the comparator 1050 according to change ofan output current value I_s of the current sensor 1040, may control arate of change of an electrical state from one state to another state.That is, the RC circuit 1060 controls a time constant τ. A voltage V_capplied to a capacitor C1 in the RC circuit 1060 cannot instantaneouslychange according to the output current I_s of the current sensor 1040.Referring to reference numeral 1060, a voltage applied to a fourthresistor R4 according to the output current I_s of the current sensor1040 can be applied to the capacitor C1 after a lapse of timecorresponding to the time constant τ. Here, the time constant iscalculated by multiplying the resistance value of R4 by the capacitancevalue of the capacitor C1. For example, when the resistance value of R4of the RC circuit 1060 is 10 kΩ and the capacitance value of C1 is 1 μf,the time constant ti may be 10 ms (10 kΩ*1 μf). That is, the voltageapplied to R4 can be applied to C1 after a lapse of 10 ms.

A predetermined reference voltage V_ref is applied to the negativeterminal of the comparator 1050 and the voltage of the capacitor C1,V_c, is applied to the positive terminal thereof. Here, the outputvoltage V_out of the DC-DC converter 1020 may be controlled according tothe output voltage V_a of the comparator 1050. The output voltage V_a ofthe comparator 1050 may be dynamically changed according to a differencebetween V_ref and V_c. Consequently, the output voltage V_a of thecomparator 1050 may be dynamically changed with a predetermined delayaccording to change in the current I_in input to the DC-DC converter1020.

Referring to reference numeral 1070, which is referred to as a voltagedistribution circuit 1070 for convenience of description, in FIG. 10,the relationship between the output voltage V_a of the comparator 1050and the output voltage V_out of the DC-DC converter 1020 is representedby the following equation 1. Referring to Equation 1, V_output isdetermined by V_a when V b is a constant. That is, V_out decreases whenV_a increases and increases when V_a decreases. The output voltage V_outof the DC-DC converter 1020 is adaptively controlled through thefeedback circuit according to an embodiment of the present invention andthus the current I_in input to the DC-DC converter 102 may be maintaineduniform.

$\begin{matrix}{\mspace{79mu} {{{{I\_}1} = {{{{I\_}2} + {{I\_}{3\lbrack {( {{V\_ out} - {V\_ b}} )\text{/}R\; 1} \rbrack}}} = {\lbrack {( {{V\_ b} - {V\_ a}} )\text{/}R\; 2} \rbrack + \lbrack {{V\_ b}\text{/}R\; 3} \rbrack}}}{{V\_ out} = {{{( {\lbrack {( {{V\_ b} - {V\_ a}} )\text{/}R\; 2} \rbrack + \lbrack {{V\_ b}\text{/}R\; 3} \rbrack} )*R\; 1} + {V\_ b}} = {{{V\_ b}( {{R\; 1\text{/}R\; 2} + {R\; 1\text{/}R\; 3} + 1} )} - {{V\_ a}\text{/}R\; 2}}}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

The wireless power control device according to the embodimentillustrated in FIG. 10 may include a feedback circuit including thecurrent sensor which detects change in the intensity of current input tothe DC-DC converter and the comparator configured to adaptively changethe voltage of the output terminal of the DC-DC converter according to adetection result of the current sensor. The intensity of current inputto the DC-DC converter can be maintained uniform through the feedbackcircuit. That is, the wireless power control device according to thepresent invention has the advantage of controlling uniform power to bereceived by a wireless power receiver irrespective of changes in thecoupling coefficient between the transmission coil and the receptioncoil.

In addition, a wireless power transmission device including the feedbackcircuit according to the embodiment illustrated in FIG. 10 can provideuniform power irrespective of rapid movement of a wireless powerreceiver by maintaining the intensity of current input to the powerconverter, that is, the DC-DC converter, uniform.

Further, the wireless power transmission device including the feedbackcircuit according to the embodiment illustrated in FIG. 10 can alsodetect the intensity of current applied to the power converter for aperiod of time in which a feedback signal is not received through afeedback channel established between the wireless power transmissiondevice and a wireless power receiver to control power rapidly andactively.

FIG. 11 is a flowchart for describing a wireless power control method ina wireless charging system according to an embodiment of the presentinvention.

Referring to FIG. 11, a wireless power transmitter 1110 may enable apower control function according to a feedback circuit when entering apower transmission state (S1101).

Upon reception of a predetermined feedback signal requesting powercontrol from a wireless power receiver 1120 during power controlaccording to the feedback circuit, the wireless power transmitter 1110may control power according to the received feedback signal (S1102 toS1104).

For example, the wireless power transmitter 1110 may continuouslyperform power control according to the feedback circuit until a secondfeedback signal is received after power control according to a firstfeedback signal.

When power transmission is stopped or charging is completed, thewireless power transmitter 1110 may disable the power control functionaccording to the feedback circuit (S1105). In the above-describedembodiment illustrated in FIG. 10, when the intensity of transmittedpower is changed according to the feedback signal, the wireless powertransmitter may control a new reference voltage corresponding to thechanged intensity of transmitted power to be applied to the negativeterminal of the comparator 1050.

In another embodiment of the present invention, when a charging mode ofthe wireless power receiver is changed through a predeterminednegotiation procedure, the wireless power transmitter may control a newreference voltage corresponding to the changed charging mode to beapplied to the negative terminal of the comparator 1050. For example,charging modes may include a normal charging mode and a high-speedcharging mode, but the present invention is not limited thereto.

In another embodiment of the present invention, when the category of thewireless power receiver is changed through a predetermined negotiationprocedure, the wireless power transmitter may control a new referencevoltage corresponding to the changed category to be applied to thenegative terminal of the comparator 1050. For example, the category ofthe wireless power receiver may be defined as shown in Table 2, but thepresent invention is not limited thereto.

In another embodiment of the present invention, when the class of thewireless power transmitter is changed through a predetermined controlprocedure, the wireless power transmitter may control a new referencevoltage corresponding to the changed class to be applied to the negativeterminal of the comparator 1050. For example, the class of the wirelesspower transmitter may be defined as shown in Table 1, but the presentinvention is not limited thereto. The class of the wireless powertransmitter may be changed when an available power amount changes or amaximum power amount required by the wireless power receiver changes,but the present invention is not limited thereto.

The wireless power transmission device according to the embodimentillustrated in FIGS. 9 to 11 may further include the controlcommunication unit 816 which establishes a communication channel with awireless power receiver, receives a feedback signal through theestablished communication channel and controls power on the basis of thereceived feedback signal.

The control communication unit (not shown) according to an embodiment ofthe present invention may control not only the operation of the feedbackcircuit 940 but also a reference voltage applied to the comparator 1050to be adaptively changed when at least one of the class of the wirelesspower transmitter and the category of the wireless power receiverchanges.

Further, the control communication unit may control operations of thedetailed components of the wireless power transmission deviceillustrated in FIGS. 9 and 10.

FIG. 12 is a flowchart for describing a wireless power control method ina wireless power control device according to an embodiment of thepresent invention.

Referring to FIG. 12, the wireless power control device may control apredetermined reference voltage corresponding to a charging modenegotiated in an initial negotiation step to be applied to a negativeterminal of a comparator in a feedback circuit (S1201).

The wireless power control device may control transmitted power to bemaintained uniform in a power transmission state using the feedbackcircuit (S1203).

When the charging mode changes during power control using the feedbackcircuit, the wireless power control device may control a new referencevoltage corresponding to the changed charging mode to be applied to thenegative terminal of the comparator in the feedback circuit (S1204 andS1205).

For example, when the charging mode changes from a normal low-speedcharging mode to a high-speed charging mode, power required by awireless power receiver may change from 5 W to 10 W. In this case, thereference voltage applied to the negative terminal of the comparator maybe doubled.

Although an example in which the reference voltage of the comparator isdynamically changed when the charging mode changes is described in theembodiment illustrated in FIG. 12, this is merely an embodiment and thereference voltage applied to the comparator of the feedback circuit maybe dynamically changed when the category of the wireless power receiver,the class of the wireless power transmitter, or the like changes inanother embodiment of the present invention.

FIG. 13 is a flowchart for describing a wireless power control method ina wireless power transmission device according to another embodiment ofthe present invention.

Referring to FIG. 13, a wireless power transmission device whichwirelessly transmits power to a wireless power reception device maydetect the intensity of current flowing between a power supply unitwhich supplies a fixed voltage and a power converter during powertransmission (S1301).

The wireless power transmission device may adaptively control the outputvoltage of the power converter according to the detected intensity ofcurrent such that the intensity of current detected between the powersupply unit and the power converter is maintained uniform (S1302).

Here, the output voltage of the power converter may be controlled by theoutput voltage of a comparator.

Further, the output voltage of the comparator may be determined by apredetermined reference voltage applied to the negative terminal of thecomparator and a voltage applied to the positive terminal thereof inaccordance with the detected intensity of current.

In addition, the voltage applied to the positive terminal of thecomparator may be a voltage applied to a capacitor of an RC circuitwhich determines a time constant.

For example, the wireless power control method may further include astep of checking whether a charging mode has changed. When the chargingmode has changed, a new predefined reference voltage corresponding tothe changed charging mode may be applied to the negative terminal of thecomparator.

Alternatively, the wireless power control method may further include astep of checking whether the class of the wireless power transmitter haschanged. When the class has changed, a new predefined reference voltagecorresponding to the changed class may be applied to the negativeterminal of the comparator.

Alternatively, the wireless power control method may further include astep of checking whether the category of the wireless power receiver haschanged. When the category has changed, a new predefined referencevoltage corresponding to the changed category may be applied to thenegative terminal of the comparator.

Further, the wireless power control method may further include a step ofcontrolling power according to a predetermined feedback signal when thepredetermined feedback signal for power control is received from thewireless power receiver during execution of the step of controlling theoutput voltage of the power converter.

Here, the feedback signal may be a dynamic characteristic parameterpacket defined in the A4WP standard and received through an out-of-bandcommunication channel.

Another embodiment of the present invention may provide acomputer-readable recording medium in which a program for executing theabove-described wireless power control methods in the wireless powertransmitter is recorded.

In this case, the computer-readable medium is distributed to a computersystem connected through a network and thus computer-readable code maybe stored and executed therein. In addition, functional programs, codeand code segments for realizing the above-described methods may beeasily deduced by programmers in the art to which the embodimentspertain.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention.

Accordingly, the above description is therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by the appended claims and their legal equivalents,not by the above description, and all changes coming within the meaningand equivalency range of the appended claims are intended to be embracedtherein.

The present invention may be used in the field of wireless charging and,particularly, applied to wireless power transmission devices.

What is claimed is:
 1. A wireless power control method in a wirelesspower transmission device for wirelessly transmitting power to awireless power reception device, the method comprising: receiving afirst control signal from the wireless power reception device at a firsttime interval; sensing a current within the wireless power transmissiondevice to generate a second control signal at a second time interval;and controlling a wireless power based on the first control signal andthe second control signal, wherein the first time interval is longerthan the second time interval.
 2. The wireless power control methodaccording to claim 1, wherein the controlling the wireless powerincludes maintaining a current within the wireless power transmissiondevice for at least a certain period of the first time interval.
 3. Thewireless power control method according to claim 2, wherein an intensityof the wireless power is controlled by converting a voltage output at apower converter of the wireless power transmission device.
 4. Thewireless power control method according to claim 3, wherein the firstcontrol signal is used by the wireless power transmission device toadjust the intensity of the wireless power.
 5. The wireless powercontrol method according to claim 4, wherein the current is input to thepower converter of the wireless power transmission device.
 6. Thewireless power control method according to claim 1, wherein the secondcontrol signal is used by the wireless power transmission device tomaintain an intensity of current transferred to a power transmitter ofthe wireless power transmission device, and wherein the powertransmitter includes a transmission coil.
 7. The wireless power controlmethod according to claim 3, wherein the second control signal is usedby the wireless power transmission device to maintain an intensity ofcurrent transferred to a power transmitter of the wireless powertransmission device, and wherein the power transmitter includes anamplification circuit for amplifying an AC signal generated using anoutput DC voltage of the power converter.
 8. The wireless power controlmethod according to claim 1, wherein the first control signal isreceived through a communication channel between the wireless powertransmission device and the wireless power reception device.
 9. Thewireless power control method according to claim 1, wherein the firstcontrol signal includes a digital signal, and wherein the second controlsignal includes an analog signal.
 10. The wireless power control methodaccording to claim 1, wherein a coupling efficiency between atransmission coil of the wireless power transmission device and areception coil of the wireless power reception device changes multipletimes within the first time interval.
 11. A wireless power transmissiondevice for wirelessly transmitting power to a wireless power receptiondevice, the wireless power transmission device comprising: acommunication and control unit configured to receive a first controlsignal from the wireless power reception device at a first timeinterval; and a feedback circuit configured to sense a current withinthe wireless power transmission device to generate a second controlsignal at a second time interval, wherein the communication and controlunit controls a wireless power based on the first control signal and thesecond control signal, and wherein the first time interval is longerthan the second time interval.
 12. The wireless power transmissiondevice according to claim 11, wherein the communication and control unitis configured to control the wireless power by maintaining a currentwithin the wireless power transmission device for at least a certainperiod of the first time interval.
 13. The wireless power transmissiondevice according to claim 12, wherein an intensity of the wireless poweris controlled by converting a voltage output at a power converter of thewireless power transmission device.
 14. The wireless power transmissiondevice according to claim 13, wherein the first control signal is usedby the wireless power transmission device to adjust the intensity of thewireless power.
 15. The wireless power transmission device according toclaim 14, wherein the current is input to the power converter of thewireless power transmission device.
 16. The wireless power transmissiondevice according to claim 11, wherein the second control signal is usedby the wireless power transmission device to maintain an intensity ofcurrent transferred to a power transmitter of the wireless powertransmission device, and wherein the power transmitter includes atransmission coil.
 17. The wireless power transmission device accordingto claim 13, wherein the second control signal is used by the wirelesspower transmission device to maintain an intensity of currenttransferred to a power transmitter of the wireless power transmissiondevice, and wherein the power transmitter includes an amplificationcircuit for amplifying an AC signal generated using an output DC voltageof the power converter.
 18. The wireless power transmission deviceaccording to claim 11, wherein the first control signal is receivedthrough a communication channel between the wireless power transmissiondevice and the wireless power reception device.
 19. The wireless powertransmission device according to claim 11, wherein the first controlsignal includes a digital signal, and wherein the second control signalincludes an analog signal.
 20. The wireless power control deviceaccording to claim 11, wherein a coupling efficiency between atransmission coil of the wireless power transmission device and areception coil of the wireless power reception device changes multipletimes within the first time interval.